This invention is directed to a molding composition comprising blends of a poly(biphenyl ether sulfone) resin. More particularly the invention is directed to improved molding resin compositions comprising a ternary blend comprising up to 50 wt % poly(biphenyl ether sulfone) resin, together with polysulfone resin and polyether sulfone resin. The ternary blends of this invention, particularly the preferred compositions, attain the very attractive thermal and environmental resistance characteristics of poly(biphenyl ether sulfone) resins, and display excellent mechanical properties.
Articles made from the ternary blends of this invention can be steam-sterilized repeatedly without stress cracking. Moreover they are not affected by corrosion-reducing additives such a morpholine, for example, and demonstrate good chemical resistance in contact with commonly used hospital cleaners and detergents.
Poly(aryl ether sulfones) have been known for nearly three decades. They are tough linear polymers that possess a number of attractive features such as excellent high temperature resistance, good electrical properties, and very good hydrolytic stability. A variety of poly(aryl ether sulfones) are commercially available, including the polycondensation product of 4,4'-dihydroxydiphenyl sulfone with 4,4'-dichlorodiphenyl sulfone described in, for example, Canadian Patent 847,963 and known in the art as poly(ether sulfone) (PES) resin, and the polymer of bisphenol-A and 4,4'-dichlorodiphenyl sulfone widely known in the art as polysulfone (PSF) resin, described in U.S. Pat. No. 4,108,837.
A third commercial poly(aryl ether sulfone) is the poly(biphenyl ether sulfone) resin, available from BP Amoco Polymers, Inc. under the trademark of Radel.RTM. R resin. This resin may be described as the product of the polycondensation of biphenol with 4,4'-dichlorodiphenyl sulfone and also is well known and described in the art, for example, in Canadian Patent No. 847,963.
Because of their excellent mechanical and thermal properties, coupled with outstanding hydrolytic stability, poly(aryl ether sulfones) have found wide application, particularly in producing extruded goods and molded articles for use where exposure to severe environments is contemplated. Parts molded from poly(biphenyl ether sulfone) resins have substantially better mechanical properties than those from other readily available poly(aryl ether sulfone) resins including PES and Polysulfone resins, and are generally more chemically resistant.
Although poly(aryl ether sulfone) resins are also highly resistant to mineral acids and salt solutions, when exposed to polar organic solvents they readily stress crack. Where increased environmental stress crack resistance is desired, blends of poly(aryl ether) resins have been employed to make them more acceptable for use in a solvent environment without substantially affecting their mechanical or electrical properties. Blends comprising polyetherimide resins and poly(aryl ether sulfone) resins are disclosed in U.S. Pat. No. 4,293,670 to have significantly improved environmental stress crack resistance and good impact strength. Environmentally resistant blends comprising poly(biphenyl ether sulfone) resins and poly(ether sulfone) resins are described in U.S. Pat. No. 5,086,130, and a variety of other blends have also been described in the art for these purposes including, for example, blends of poly(aryl ether sulfones) with polyamide-imides as well as blends with poly(aryl ether ketones). Copolymers with improved stress-cracking resistance are also known in the art including, for example, co-poly(biphenyl ether sulfone) resins comprising bisphenol A moieties as disclosed and described in U.S. Pat. No. 5,164,166.
Poly(biphenyl ether sulfone) resins are known for their good mechanical properties at elevated temperatures and they have excellent high temperature stability. These resins may be combined with suitable flame retardant additives to provide highly desirable chemically-resistant, flame retardant, low heat release materials for use in aircraft interiors and the like, as disclosed in U.S. Pat. No. 5,204,400, and are particularly useful for these purposes when employed in blends with poly(arylether ketones).
Because of their excellent mechanical and thermal properties, coupled with outstanding hydrolytic stability, the poly(aryl ether sulfone) resins have been utilized in the medical market for a variety of medical devices for at least ten years. One of the major requirements for materials used in such devices is the ability to be steam autoclaved repeatedly without loss of properties. Steam autoclaving is a very severe test, requiring both high temperature and hydrolytic stability, and involving cyclical effects--wet/dry, hot/cold. The poly(aryl ether sulfones) known as PES and PSF show some important deficiencies in this regard. Parts molded from these materials stress-crack when steam sterilized under stresses of say 500 psi or greater, especially when excessive concentrations of boiler additives such as morpholine are employed to reduce corrosion in the steam generating system, or when placed in contact with commonly used hospital cleaners and detergents.
Poly(biphenyl ether sulfone) resins and parts molded therefrom are widely recognized to have substantially better properties than PES or PSF resins in this regard. However, these resins are substantially more expensive than PES or PSF resins due to the high cost of biphenol. Considerable effort has gone into developing lower cost materials for medical uses with resistance to chemical and environmental attack equivalent to that of poly(biphenyl ether sulfone) resins. In U.S. Pat. No. 5,164,466 blends of poly(biphenyl ether sulfone) resins with polysulfone resins are disclosed to have substantial resistance to steam sterilization only at a high level of the poly(biphenyl ether sulfone) component. Similarly, blends comprising poly(biphenyl ether sulfone) and PES resin, disclosed in U.S. Pat. No. 5,086,130, do not have the requisite environmental stress crack resistance when the poly(biphenyl ether sulfone) component is less than about 40 wt %. Blends presently available for use in medical applications thus will necessarily be formulated to contain a major proportion of the more expensive poly(biphenyl ether sulfone) resin. Development of improved materials having the desired combination of mechanical properties and chemical resistance for use in the production of steam sterilizable articles suitable for medical uses would be an important advance in the resin arts.